The Differential Thermal Analysis of Ore Minerals (III) : On Minerals of the Systems Bi-Sb-S and Cu-Sb-As-S

A series of the studies on the thermal behavior of sulfide minerals has heen studied by the authors by means of the differential thermal analysis (DTA) in these several years. This paper is the third report of the series and includes the DTA curves and some discussions about synthetic and natural minerals belonging to the Bi-Sb-S and the Cu-Sb-As-S systems. The analysis was carried out for the sample of 400-600mg in weiht which was sealed in a evacuated silica glass tube. The heating rate was 5℃/min. in regular analysis but the rate of 1.25℃/min. was adopted in some cases to determine a more detailed reaction and to know the temperature of the reaction more precisely. The DTA curves for synthetic phases of the Bi_2S_3-Sb_2S_3 system are shown in Fig. 1. Synthetic bismuthinite and stibnite, end member of this system, show sharp endothermic peaks beginning at 765℃ and 558℃ respectively, but the curves of the phases such as between these two show typical melting reactions of solid solution. The DTA curves of natural stibnite (Fig. 2), as well as that of synthetic stibnite are supposed to indicate a congruent melting. Natural bismuthinite from Teine mine does not show a sharp endothermic peak as synthetic one, and its curve suggests some characteristics of solid solution melting like that of horobetsuite (Fig. 3). The remarkable endothermic peaks of the congruent melting reaction beginning at 551℃ and 613℃ are seen on the DTA curves for synthetic chalcostibite and stylotypite respectively (Fig. 4). A series of synthetic tetrahedrite-tennantite group minerals having different compositions are analysed and the results are shown in Figs. 5-8. Their DTA curves except Cu_<12>Sb_4S_<12.7> show that they might have a melting reaction of solid solution, and the beginning temperature of the melting changes by their compositions. Namely, the temperature is ascending with increase of Fe content, and descending with increase of Ag content. Also it is getting higher with increase of tennantite molecules in the synthetic minerals of the tetrahedrite-tennantite group. The DTA curves of the natural minerals of the group are showing the relationship as mentioned above (Fig. 9). Both of synthetic and natural enargite produce a single remarkable endothermic peak beginning around 670℃ as shown in Fig. 10. On the DTA curves for natural luzonite-famatinite group minerals, some differences of the melting temperature and/or the type of melting are observed depending on their compositions (Fig. 11). The curves of luzonite from Lepanto and from Mancayan, having composition poor in famatinite molecule, show congruently melting reactions, but those from Kinkaseki and from Teine, rich in famatinite molecule, indicate some character of solid solution melting. The former shows higher melting temperature than the later. The transformation reaction from luzonite to enargite, which is expected around 320℃, has not been seen in any curves of luzonite.